1. Field of the Invention
The present invention relates generally to a process for producing multilayered bulk material. More specifically, it relates to a production method of multilayered bulk materials, based on a combined technique of mechanically alloying and subsequent hot pressing, by which the thickness and interlayer distance of the layer structure can be chosen as thick as possible.
2. Brief Description of the Related Art
The anisotropy--physical properties change with the direction along which a measurement is made--is one of intrinsic properties of multilayered materials. Due to the property, multilayered materials have attracted much attention from industry and academic side.
Physical properties of a material are generally dependent on whether the material is in the shape of two-dimension or three-dimension. Each layer of a multilayered material has its different characteristics, depending on its thickness. Based on the characteristics of each layer, the multilayered material has peculiar characteristics compared to non-multilayered materials.
Anisotropy of the physical properties according to whether the direction is vertical or horizontal, is one of unique properties of a mutlilayered materials. Because of the property, multilayered materials have been used as multi-functional materials. Therefore, it is expected that multilayered materials will be sources for new materials having desired multi-functions, which has been impossible to achieve with non-multilayered materials.
In prior art methods, multilayered materials are prepared by means of evaporation, sputtering, or iodine vapor transport reaction, but these processes are subject to thickness limitations, i.e., individual layers are thin films of submicron (less than about 100.about.300 .ANG. in thickness)
In the case of both evaporation and sputtering, which are kinds of physical vapor deposition (PVD) where constituting atoms are deposited on a substrate, individual layers are generally less than about 100.about.300 .ANG., and the production cost is high.
The method of iodine-transport reaction has limited applicability in that it can be applied only to a particular class of organic metals. In addition to high production cost, the method is also subject to thickness limitation (less than 10.about.30 .ANG.). The prior art processes for making multilayered materials are subject to several limitations including thickness, thereby causing many practical problems.